1. Field of the Invention
The present invention relates to improvements in heating apparatus for a motor vehicle passenger compartment.
2. Description of the Prior Art
An apparatus for heating passenger compartments of motor vehicles is generally includes a heat exchanger disposed within the passenger compartment that is supplied with a high temperature liquid which has been used for cooling various portions of the engine.
With this type of apparatus, since liquid circulating through the heat exchanger is heated only when the engine is running subsequent to engine start-up, a considerably long period of time is required to raise the liquid temperature within the heat exchanger.
In order to solve the above problem, a heating apparatus is proposed wherein a heater, such as an external combustion heater, is provided to heat the liquid prior to engine start-up and to compensate for insufficient heat produced by the engine.
However, according to this type of conventional heating apparatus, it is necessary to warm up a considerably large amount of liquid held within an engine water jacket, the heat exchanger and a feed passage, by means of heat produced by the engine or the external combustion heater. A problem is still encountered in that liquid temperature does not rise rapidly, requiring considerable time to raise the temperature within the passenger compartment.
Furthermore, since the liquid is also utilized for the heater during engine idling, it is necessary to raise engine idling speed to shorten the liquid warm-up period. However, raising engine idling speed for improved heat generation results in increased fuel consumption.